Electrode and method of making the same



Feb. 23, 1937 w. H. WELCH ELECTRODE 'AND METHOD OF MAKING THE SAME Filed Jan. 26, 1934 Snventor Wimom H. Welsh attorneys Patented Feb. 23, 1937 UNITED STATES ELECTRODE AlTqnBEMETfloD OF MAKING SAME William H. Welch, Cuyahoga Falls, Ohio, assignor to The Firestone Steel Products Company, Akron, Ohio, a corporation of Ohio Application January 26, 1934, Serial No. 708,407

2 Claims.

This invention relates to electrodes and to methods of making the same, and more especially it relates to electrode wire that normally is subject to great heat, for example, the electrodes of the spark plugs of internal combustion engines.

Due to severity of conditions incidental to the use of spark plugs, the electrodes of ordinary spark plugs are subject to inter-granular corrosion and rapid disintegration or burning away, which requirethat periodic adjustment be made to preserve eflicient sparking at the gap and I which limits the life of the plug in service. Tests show that the ordinary spark plug electrode sponges out during use, and becomes larger in cross section due to inter-granular corrosion, with the result that the granules or crystals on the surface of the electrode lose their cohesion and flake off, thus causing rapid deterioration of the electrode.

The'chief objects of the invention are to provide an improved electrode of the character mentioned, that will have relatively long life; that .will resist corrosion; and to provide a method of making such an electrode. Other objects will be manifest.

In achieving the foregoing objects it was found that the structure, particularly grain size and shape of the grains of the electrode wire, was of primary importance, the composition of. the alloy being secondary thereto. Best results were obtained where the grain size was relatively small both longitudinally and in cross section, apparently for the reason that since corrosion follows the inter-granular boundaries, the smaller. grain size has greater resistance to attack.

Of the accompanying drawing:

Figure 1 is a photomicrograph of a transverse section of the improved electrode, magnified 200 diameters;

Figure 2 is a view on the same scale as Figure 1, of a longitudinal section of the improved electrode;

Figure 3 is a view on the same scale as Figure 1, of a transverse section of an ordinary prior art electrode;

Figure 4 is a view on the same scale as Figure 1, of a longitudinal section of an ordinary prior art electrode; and R 'Figure 5 is a side elevation of a spark plug comprising the improved electrode.

It is known that small percentages of certain metals alloyed with nickel retard interegranular corrosion. Preferably the alloy used in the improved electrode is of the following composition:

Per cent Manganese 3 .90-4 .25 Silicon .75 1.00 Cobalt max .25 Carbon max .06 Sulphur -max- .03 Iron max .25 Nickel Balance The percentages may be varied slightly without appreciable detrimental effect. This alloy is substantially standard for the usual spark plug electrodes, and no novelty is claimed for it.

In the manufacture of electrode wire from metal of the foregoing composition, the alloy first "is cast in ingot form, which ingot is then rolled into a bar'and the latter drawn through successively smaller drawing dies until the desired wire size is reached. Between each pass or drawing operation the wire is annealed by heating at a temperature of 1200 F. to 1550 F., the time and temperature of annealing being carefully controlled to prevent grain growth. In order that the minimum grain size may be obtained in the finished product, the reduction in all drawing operations is very carefully controlled. Too great reduction in any of the passes would necessitate excessive annealing, which is objectionable in that it promotes grain growth. Experience has shown that about 25% reduction of the wire on each pass throughv the dies gives satisfactory results.

While the process may be carried out by the usual method of intermittent drawing and pot annealing,fit is particularly adapted for a continuous method of drawing and annealing. the latter step being carried out in an elongated furnace through which the wire is continuously passed.

Just before the final drawing operation. the wire is given a special heat treatment which consists in soaking at the critical temperature of recrystallization, within a range of 1200 F. to 1600 F. according to a duration of treatment of 6 hours to 2 hours respectively in the case of treatment of arch of wire by the pot annealing process, depending .upon the, amount of wire treated and the container in which it is placed. Preferably the wire is treated about 2 hours at 15.50". In the continuous annealing and drawing process a lesser time of heat treatment is required due.to the relatively smaller mass presented and to the relatively larger heater volume.

It has been found that if the wire is heated below the proper temperature or for too short a in final form presents a smooth, bright and clean surface free from slivers or flaws.

Referring now to the drawing, Figure shows a spark plug. l0 having electrodes H and I2, both of which preferably consist of the improved electrode wire. Micro analysis shows the improved electrode wire to be composed of grains of one one-hundredth (1/100) to one three-hundredth (1/300) the grain size of the ordinary electrode wire for the same purpose. The relative smallness of the grains of the improved wire as compared to the grains of prior structures will be apparent from a comparison of Figures 1 and 2 with Figures 3 and 4 respectively. In a grain count made on a photomicrograph' of the improved electrode wire at 200 diameters, such as Figure 1, a 2-inch diameter circle representing an area of 100 circular mils will contain at least .200 grains. Moreover, the grains of the improved wire are egui-axed, that is, the particle size is substantially the same transversely as longitudinally. It has furthermore been found that g has its grain and crystalline structure in equitime it would not be properly annealed, and if The wire is finished in the usual manner andelectrode wire treated by this improved process a correspondingcoarse-grained wire. The latter also would have a rough or pebbly surface. Ac-

tual tests have shown that the use of the improved electrode greatly prolongs the life of spark plugs in service.

Modification may be resorted'to without departing from the spirit of the invention or the scope of the appended claims, which are not limited wholly to the specific construction shown or exact procedure described.

What is claimed is:

1. The method of making electrodes which comprises drawing an ingot of nickel alloy to wire form, and before the last drawing operation subjecting the wire to a heat treatment consisting of soaking it at the critical temperature of recrystallization within a range of 1200 F. to 1600 F. according to a duration of treatment. of 6 hours to 2 hours, respectively.

2. The method of making electrodes which comprises drawing an ingot of nickel alloy to wire form, and before the last drawing operation subjecting the wire to a heat treatment consisting of soaking it at the critical'temperature of recrystallization within a range of 1200, F. to 1600 F. according to a duration of treatment of 6 hours to 2 hours, respectively, for a sufficient period to produce a grain structure in the alloy, the grains of which are equi-axed. 

